In recent years, with a reduction in a size of an electronic component and an increase in a density, a double-sided board or a multilayer board is frequently used as a circuit board to be provided with an electronic component in place of a conventional single-sided board. As a structure of the circuit board, furthermore, an inner via hole structure is proposed in place of a connection of layers by a through hole processing and plating which are conventionally used widely. The inner via hole structure indicates a method of connecting layers by using a conductive paste, and high density wiring can be obtained. A method of manufacturing a circuit board using the conductive paste will be described with reference to FIGS. 14A to 15C. FIGS. 14A to 14D are sectional views for explaining the method of manufacturing a circuit board by using the conductive paste.
FIG. 14A shows a section of prepreg 1 having protective film 2 provided on both sides. FIG. 14B shows a state in which hole 3 is provided on prepreg 1 illustrated in FIG. 14A. FIG. 14C shows a state in which prepreg 1 having hole 3 formed thereon is fixed to base 6 and jig 4 of a squeegee formed by rubber (or a rub-in rubber plate) is moved in a direction of arrow 7 to fill hole 3 with conductive paste 5. FIG. 14D shows a state in which protective film 2 is peeled from both sides of prepreg 1 and protruded portion 8 formed by conductive paste 5 is provided.
FIGS. 15A to 15C are sectional views for explaining a method of manufacturing a both-sided board using a conductive paste, illustrating subsequent steps to FIG. 14D.
FIG. 15A shows a state in which copper foil 9 is disposed on both sides of prepreg 1 provided with protruded portion 8, and pressurization and integration are carried out as shown in arrow 71 by using a press device (not shown). In the integration, heating is also useful. By providing protruded portion 8 on conductive paste 5, it is possible to compress and bond conductive powder particles contained in conductive paste 5 at a high density.
FIG. 15B is a sectional view showing a state brought after copper foil 9 is integrated through prepreg 1 or conductive paste 5. In FIG. 15B, insulating layer 10 is formed by heating and curing prepreg 1. In via 11, the conductive powder particles contained in conductive paste 5 are compressed, deformed, and bonded to each other.
FIG. 15C shows a state in which copper foil 9 of FIG. 15B is subjected to etching to form wiring 12 having a predetermined pattern. Then, a solder resist or the like (which is not shown) is formed so that a double-sided board is manufactured.
Patent Documents 1 and 2 are known as prior art documents related to the present invention.